Businesses or other entities having a need for volume printing typically purchase a production printer. A production printer is a high-speed printer used for volume printing (e.g., one hundred pages per minute or more). Production printers are typically continuous-form printers that print on webs of print media which are stored on large rolls.
A production printer typically includes a localized print controller that controls the overall operation of the printing system, and a marking engine (sometimes referred to as an “imaging engine” or as a “print engine”). The marking engine includes one or more printhead assemblies, with each assembly including a printhead controller and a printhead (or array of printheads). An individual printhead includes multiple tiny nozzles (e.g., 360 nozzles per printhead depending on resolution) that are operable to discharge ink as controlled by the printhead controller. A printhead array is formed from multiple printheads that are spaced in series across the width of the print media.
When in operation, the web of print media is quickly passed underneath the printhead arrays while the nozzles of the printheads discharge ink at intervals to form pixels on the web. In order to ensure that ink does not dry onto the printheads during printing (which would adversely affect print quality), flush lines are printed at page boundaries on the web. These flush lines are used to flush ink from each of the nozzles (i.e., across the entire width of the web) on a regular basis to ensure that the ink does not become overly viscous.
Additionally, many printing systems utilize one or more control marks to guide the actions of post-processing equipment at the print shop. For example, a printing system may add control marks onto a web to indicate where to cut the web to form pages, how to stack groups of pages, and how to perform other post-printing activities.
Unfortunately, the sensors that trigger actions at post-processing equipment may use simple heuristics, such as optical density, to detect control marks on the page. This means that flush lines can be mistakenly interpreted as control marks by post-processing equipment, which can result in the print job being cut, stacked, hole-punched, etc. at the wrong location.